The research is a first step in a more global project aimed at a systematic analysis of the flow of information through vestibular pathways, and its integration with somatosensory inputs, from vestibular nuclei to cerebral cortex. Ultimately, behavioral studies will be employed parallel to neurophysiological work to determine the contribution of vestibular-somatosensory interactions to perception of the body and its position in space. Afferents innervating the labyrinthine receptors, somatosensory pathways, and cerebellar outputs interact via vestibular nuclei neurons as a functional system or systems, probably both in specification of reflex connections, as well as in rostral projections of the vestibular system. The intent of the experiments outlined is to quantitatively characterize the response of vestibular nuclei neurons to head tilt both in the absence and presence of somatosensory and cerebellar inputs. The response functions of these neurons will subsequently be compared with already published response functions of first order neurons innervating the maculae to determine: first the nature of the transfer functions describing the transmission of head position information from first to second order neurons in the vestibular pathways; and second, to describe the extent and characteristics of convergence between vestibular and somatosensory systems in second order neurons. The significance of the proposed research is threefold: first to quantitatively characterize the information flow in this sensory system; second, to further define the already established close relationship between the vestibular and somatosensory systems; and third, to further examine the correlation of physiologically functional subdivisions of the vestibular nuclear complex with already anatomically established subdivisions.